01 General Control Valves Training.

Engineering Centre of Excellence
ECoE - Doha, Qatar

Instrument training – 16th July 2011
General Control valves.

Prepared by: Gavhane D.V.


BY:-DNYANESHWAR GAVHANE

General Control Valves. Prepared by: Gavhane D.V. 2


INTRODUCTION :-

Control valves also called final control element are a most
important element in the control system of a process plant.
It is the last device in control loop.

DEFINITION :-

A control valve is a variable orifice used to regulate the flow
of a process fluid in accordance with requirement of process.

FUNCTION :-

It absorbs the proper amount of pressure drop to maintain
system balance under all operating conditions.


Features of Control valves.
THERE ARE FOUR FEATURES OF CONTROL VALVES :

Capacity
Rangeability
Characteristics
Pressure drop

CAPACITY : The capacity is normally measured as Cv
(Flow Coefficient) which is defined as :

“The number of US gallons per minute of water at 60oF that
will flow through a valves with 1psi pressure drop .

RANGEABILITY : Rangeability of a Control Valve is the
ratio of the maximum to the minimum controllable flow.


Control valves and Flow Characteristics.
The relationship between control valve capacity and valve stem
travel is known as the Flow Characteristic of the control valve.

The Curve shown are based on constant Pressure drop across
the valve and called Inherent flow characteristics.


Linear Characteristics.
Flow Capacity increases linearly with valve (stem) travel. In
which the valve differential pressure drop is Constant over the
travel range.
Linear valve plug shall for liquid level control and control
application requiring constant gain.

LINEAR VALVE TRAVEL IS DIRECTLY PROPORTIONAL TO
THE VALVE STROKE

MORE THAN
FOR SLOW 40%
FLUID OF SYTEM
TRANSFER PRESSURE
PROCESS DROP
ACROSS
VALVE


Equal Percentage Characteristics.
Flow Capacity increases exponentially with valve trim travel .Equal
increment of valve travel produce equal percentage change in
existing Cv.
Equal Percentage valve plug shall be used where only small
percentage of system drop is available in Control valve.

EQUAL INCREMENT OF VALVE TRAVEL PRODUCE AN
EQUAL PERCENT FLOW CHANGE

FOR FAST FLIUD HIGH
TRANSFER RANGEABILITY
PROCESS


Quick Opening Characteristics.
Provides large changes in flow for very small changes in lift or in
which a maximum Cv is achieved with minimal closure member travel.
It has too high valve gain.

LARGE INCREASE IN FLOW WITH A SMALL CHANGE IN VALVE
STROKE

Quick opening valve are usually specified for “ON-OFF” Service such
as sequential operation in either batch or semi continuous process
and in self actuated control valve .
When maximum valve capacity must be obtain quickly.

Cage- A part of a valve that surrounds the
closure member & can provide Quick
opening flow characterization.

General Control Valves. Prepared by: Gavhane D.V.
8

Cavitation.
Cavitation is condition that occurs in liquid flow where the internal
pressure of liquid at set point falls below vapour pressure and vapour
bubbles form and at downstream rises above vapour pressure again.
As this pressure recovers so that bubbles collapse and cavitation take
place.
It is possible to predict where cavitation will occur by looking pressure
condition and valve recovery factor.( sigma Method )
Cavitation sounds like stone passing through the valve.
PRESSURE PROFILE ACROSS
P SINGLE SEATED CONTROL
VALVE

P

Pv

Bubble collapse
Bubble form
Vena Contracta

Effect of Cavitation.

Erosion in rotary plug valve body induced by cavitation


Flashing.
Flashing is condition that occurs with liquid flow where the Pressure fails
below it . There are then two phases flowing ( i.e. Liquid and vapour )
down stream.

Several damage can occur inside a valve due to erosion caused by the
impact of liquid droplet traveling at high speed.

P1 PRESSURE PROFILE ACROSS
SINGLE SEATED CONTROL
VALVE

Pv

Bubble form
P2 Bubble continue
down stream

Vena Contracta

Effect of Flashing.

Typical trim erosion damage due to flashing


Velocity Profile across Single seated Valve.
P1 PRESSURE PROFILE ACROSS
SINGLE SEATED CONTROL
VALVE

Pv
P2

V2
V 1(Liquid) (Liquid)

Pressure Recovery:- At vena contracta,the velocity is greatest & substantially
decrease in pressure .Further down stream, as the fluid stream expands into
a large area, Velocity decreases and pressure increases. This phenomena is
called Pressure recovery.
As a general ,globe valves have Lower pressure recovery than Ball and
Butterfly Valves.


Piping Influence/Reynolds Number/Choked Flow.

Piping Influenence:- Capacity reduction due to the presence of Reducer Up &
Down stream of the valve. Correction factor will be available from
manufacturer .
Reynolds Number :- For Reynolds number application such as viscous or
small flow , the basic sizing equation can not be used without
correction, since the equation is based on turbulence flow . Correction factor
will be available from manufacturer .(The ratio of dynamic forces to viscous
forces)
Usually the correction can be ignored when Reynolds number is greater than
4000,the correction will be 10% or less .
Choked Flow:- When the pressure at vena contracta drop below the vapor
pressure of the liquids, bubbles will form in the stream .The formation of
bubbles causes a crowding condition at vena contracta which tends to restrict
flow, and further increase in pressure drop will not produce increase in flow.
In case of gas , choked flow means outlet velocity reaches sonic velocity.
The limiting Pressure difference ΔPt is called Maximum allowable differential
pressure for sizing.


Contents of Control Valve:– Data Sheet
PROJECT:- GPS DOC NO:- -

SUB CONTRACTOR
CONTRACT NO:-
DOC NO:-
SHEET NO:- 1 OF 1

DOCUMENT SPECIFICATION AND DATASHEETS DATE:-
CLIENT DOC NO:-
NAME:- FOR CONTROL VALVES REV NO:-

DATASHEET - CONTROL VALVES
1 TAG
GENERAL
DATA

2 SERVICE BLANKET FUEL GAS FROM OIL STORAGE TANK 0-T-3603
3 LINE NO. / PID NO. 0-14"-FG-43 0017-AA3-H(E) / S2-01-YS207019-PID-P-5004 Sht 1 of 2
4 FLUID TANK VENT/FUEL GAS CRITICAL PRESS. Pc
5 UNIT MAX FLOW NORM FLOW MIN FLOW SHUT-OFF
6 FLOW RATE m3/h 5166 1847 525.3 -
7 INLET PRESSURE psi(g) 0.0568 0.093 0.0975 15 bar(g)
8 OUTLET PRESSURE psi(g) 0.037 0.0087 0.00234
SERVICE CONDITION

9 INLET TEMPERATURE Degree C 50 50 50 100(Note 1)
- /kg/m3 /
10 SPEC WT/DENSITY/ MOL WT /-/1.378/40.30 /-/1.378 /40.30 /-/ 1.381/40.30 -
kg/kmole
11 VISCOSITY /SPEC HEAT RATIO Cp / 0.00924/1.133 0.00924/1.133 0.00924/1.133 -
12 VAPOR PRESSURE inH2O NA NA NA -
13 REQUIRED CV -
14 TRAVEL % 0
15 ALLOWABLE /PREDICTED SPL dBA < 85/ < 85/ < 85/ -
16 SET POINT inH2O(g) 2.75 2.75 2.75


Contents of Control Valve:– Data Sheet.
SINGLE-ACTING FAIL SAFE
17 PIPE LINE SIZE & IN 14" & SCH20 56 TYPE SPRING RETURN –DIAPHRAGM
TYPE
LINE

SCHEDULE
18 OUT 14" & SCH20 57 MFR & MODEL VTS
HEAT CONSERVATION
19 PIPE LINE INSULATION 58 SIZE / EFF.AREA VTS
(ELECTRICAL TRACING)
20 VALVE SIZING ISA S75.01 59 ON/OFF MODULATING YES
SPEC.& CODES

ACTUATOR (PNEUMATIC)
VALVE SEAT LEAKAGE
21 IV AS PER FCI 70-2 60 SPRING ACTION ON FAIL CLOSE
CLASS
MAX ALLOWABLE
22 61 VTS
PRESS.
23 62 MIN REQUIRED PRESS. VTS
24 63 AVAILABLE AIR SUPPLY MIN NOR MAX DESIGN
25 TYPE BUTTERFLY 64 PRESSURE kPag 400 850 900 1000
26 SIZE VTS 65 BENCH RANGE VTS
ACTUATOR
27 MAX PRESS./TEMP. VTS 66 VTS
ORIENTATION
28 BODY/BONNET MATERIAL A105 or A216 WCB 67 HANDWHEEL TYPE YES VTS
AIR FAILURE LOCK
29 LINER MATERIAL / ID 68 REQD. SET AT Note 5
RELAY
30 69 AIR BOTTLE REQD. WITH ACCESSORIES
VALVE BODY

31 END CONNECTION IN/ OUT FLANGED 70 FIRE SAFE YES
32 RATING & FLANGE FACE FINI. 150# RF ASME B16.5 71 INPUT SIGNAL 4-20 mA
33 END EXTENSION/MATERIAL ASTM A105 carbon steel 72 TYPE ELECTRO-PNEUMATIC (HART)
POSITIONER EXPLOSION
34 FLOW DIRECTION YES 73 EExd
PROTECTION
ON INCR SIGNAL
35 TYPE OF BONNET BOLTED 74 FIELD REVERSIBLE
OUTPUT INCR/DECR
36 LUB & ISO VALVE / LUBE 75 GAUGES Yes BYPASS Yes
37 PACKING MATERIAL PTFE 76 CAM CHARACTERISTIC
38 PACKING TYPE VTS 77 MFR & MODEL VTS
SWITC

39 VTS 78 TYPE - QTY -
HES

BONNET GASKET
40 MFR & MODEL VTS 79 MFR & MODEL -


Contents of Control Valve:– Data Sheet .
41 TYPE VTS 80 CONTACTS/RATING -

42 SIZE RATED TRAVEL VTS VTS 81 ACTUATION POINTS -

43 CHARACTERISTIC VTS 82

44 BALANCED/UNBALANCED VTS 83 MATERIAL DIE CAST ALUMINIUM

RATED CV VTS FL VTS XT VTS 84 FILTER SIZE < or = 25 Micron
TRIM

45

AIR FILTER
46 PLUG/BALL/DISC MATERIAL F6 85 SET PRESSURE
F6 SEAT HARD FACED WITH INTEGRAL PRESS.
SEAT MATERIAL 86 50mm DIAL
47 STELLITE6. GAUGE

48 CAGE/GUIDE MATERIAL VTS 87 CONNECTION 1/2"NPT

49 STEM MATERIAL F6 88 MFR & MODEL VTS

50 89

51 NEC CLASS GR. DIV. 90 HYDRO PRESS. YES
ACCESSORIES
SPECIALS /

52 IEC ZONE GR. TEMP. CLASS CLASS I, ZONE 2 , GROUP IIA & T3 91 SEAT LEAKAGE TEST YES

TESTS
53 92 CAPACITY TEST YES

54 93

55 94

NOTES : VTS-Vendor To Specify


Globe Control Valve Construction. .


General Control Valve Classification.

CONTROL VALVE

LINEAR ROTARY
MOTION MOTION

Eccentric plug
Diaphragm valve GLOBE VALVE Butterfly
Gate valve Globe Ball
Angle
Three way


General Types of Control Valve.
CONTROL VALVE TYPES

VALVE TYPES BASED ON PLUG CONSTRUCTION ARE

GLOBE VALVE BALL VALVE BUTTERFLY VALVE

Control:- Linear & equal % Control:- Quick opening Control:- Linear & equal %
Use:- Throttling Service, And linear. Uses:- Fully open / closed or
Flow Regulation, Frequent Uses:- Fully open / closed Throttling services, Frequent
Operation limited-throttling Operation, Minimal fluid
Application:- Liquid, Vapour, Application:- Most liquids Trapping in line.
Gases, Corrosive Substances High temperature, slurries Application:-Liquids, gases,
Slurries. Advantage:- High capacity Slurries, Liquids with
Advantage: Efficient throttling Low leakage and Maint. suspended Solids.
Available in multiple ports. Tight sealing with low torque Advantage :- High Capacity
Accurate Flow control. Disadvantage:- poor Good flow control, Low Press.
Disadvantage: High pressure Throttling characteristics Drop, Low cost and Maint.
Drop, more expensive. Prone to Cavitation Disadvantage:- High torque
Required for control
Prone to cavitation at lower
ECENTRIC PLUG / CAMFLEX DIAPHRAGM KNIFE GATE
Flows.


Eccentric Plug / Camflex Valve Construction.

Side view of an eccentric plug valve
Shown in partially open…..


Eccentric Disk/Ball/Knife Valve Construction
Eccentric Disk Valve V-Notch Ball Valve Knife Gate Valve


Butterfly/Angle/Three Way Valve Construction


Diaphrgm Type Valve Construction.

Seal over a seat ( Straight type)

Weir type ( Saddle type)


General Types of Actuators .
Actuator is the part of the valve that responds to the applied signal and
causes modification of the fluid flow through stem & plug.
TYPES OF ACTUATORS:
1) Diaphragm Actuator
Direct Acting
Reverse Acting
Size depends on output thrust required and supply air pressure
available.
2) Piston Actuator
Use of high pressure air to 150 psig., eliminating the need of pressure
regulator.
Used where High & Fast Stroking Speed is required.
3) Electro hydraulic Actuator:
Electro-hydraulic Actuator is single unit contains Hydraulic Pump
and Reservoir & Electric Motor.
Ideal for isolated locations
4) Manual Actuator
Used where no auto control is required

Direct – Acting Actuators .


Actuators Fail-Safe Requirements.
Fail Safe is the action of the actuator by which the valve CLOSES (FC)
or OPENS (FO) fully in case of air supply failure.


General Types of Bonnet & Accessories .
Bonnet -
Bonnet is a part of the valve body assembly through which the valve
plug stem or rotary shaft moves.
Types Of Bonnets
Plain or Std Bonnet :-Operating Temp below 2000 c.
Finned Bonnet :- Operating Temp above 2000 c or Equal.
Extension Bonnet :- Operating Temp below 00 c or Equal.
Extension Bonnet :- Operating Temp above 4500 c.
Bellow Seal Bonnet :- where no stem leakage is tolerated For Toxic,
Expensive Fluids.

General Control Valve - Accessories
•Positioners
•Limit Switches
•Solenoid Valves
•Position Transmitters
•Volume Boosters


General Construction of Bonnet .
Forged –Valve Finned Extension Bellow Seal
Bonnet Bonnet Bonnet Bonnet ( Enviro Seal)

Std./ plain
Bonnet


Control valves Characteristics.
PROCESS APPLICATION INHERANT
CHARACTERISTICS
PRESSURE LIQUIDS EQUAL %
GAS (LOW FLOWS ) EQUAL %
GAS (LARGE FLOWS)
ΔPmax/Δpmin < 5 LINEAR
ΔPmax/Δpmin > 5 EQUAL %
Temperature Liquids & Gases EQUAL %

Flow Load Changes EQUAL %
Set point change LINEAR

Level ΔPmax/Δpmin < 5 LINEAR
ΔPmax/Δpmin > 5 EQUAL %


Control valves :- Interface

PROCESS INTERFACE
Process to provide process data to Instrument for specifying the
valve
Instrument to provide slected valve size to Process for
incorporating in P&IDs
Instrument to provide instrument air consumption figures for the
valves to Process to decide air line & header sizes.
PIPING INTERFACE
Instrument to provide Face to Face Dimensions, End Connection
Size & Rating, Actuator Height & Orientation, Envelope
Dimensions (for 3-D Model), Weight, etc.
Piping to provide location of control valves to Instrument for
deciding instrument air manifolds.
Piping to provide Pipe Material Specification to Instrument for
specifying the valves.


Control valves Body Material.
Frequently Used Valve Body Cast Materials Are:
CARBON STEEL (ASTM A216 GR WCC) up to 4270 C
CHROME MOLY STEEL (ASTM A217 GR WC9) up to 5930 C
CARBON MOLY STEEL (ASTM A217 GR C5) up to 5930 C
304L STAINLESS STEEL (ASTM A351 GR CF3) up to 8160 C
316 STAINLESS STEEL (ASTM A351 GR CF8M) up to 8160 C
CAST IRON (ASTM A126) up to 2320 C

Special Materials Used Depending On The Process Requirements
HASTEALLOY B
HASTEALLOY C
MONEL ALLOY


Control valves Trim Material.

Frequently Used Valve Trim Materials Are:
• 302 SS : ASTM A 276 TYPE 302
• 304 SS : ASTM A 276 TYPE 304
• 316 SS : ASTM A 276 TYPE 316
• 316 L SS : ASTM A 276 TYPE 316L
• 410 SS : ASTM A 276 TYPE 410
• 17-4 pH SS : ASTM A 461 GR 630
[High Tensile Strength, High Yield point, Hardened Material]
• HASTEALLOY ``B’’ : ASTM A 335
• HASTEALLOY ``C’’ : ASTM A 336


Control valves Codes and Standards.
ANSI B 16.34 :
• Covers Pressure, Temperature rating, Dimensions, Materials, NDT
Requirements
ANSI B 16.5 :
• Covers design of flanges and flanged fittings
MSS SP 67 :
• Covers design and test performance requirements of Butterfly valves and
divides in to three leak classes.
ANSI B 16.10:
• Face to Face dimensions
ANSI B 16.37:
Hydrostatic testing
LEAKAGE RATES AS PER ANSI/FCI 70-2
Formerly (ANSI B 16.104) for seat leak classes and testing procedures
- FCI


Vendor Design Documents- Sizing & Selection
Step # 1:- Define the system
Example :- The system is pumping water from one tank to another through a
piping system total pressure drop is 150psi.The fluid is water at 700F.Design
(maximum) flow of 150 gpm,operating flow rate of 110 gpm,and minimum flow rate
of 25gpm. Pipe diameter is 3 inches. At 700F, water has has a specific gravity of1.0
Key Variables:- Total pressure drop , design flow ,operating flow, minimum flow
diameter, specific gravity.

Step # 2:- Define Max. Allowable Pressure Drop For The Valve
When defining the allowable pressure drop across the valve, you should first
investigate the pump.What is its maximum available head? Remember that the
system pressure drop is limited by the pump. Essentially the Net Positive Suction
Head Available (NPSHA) minus the Net Positive Suction Head Required (NPSHR)
is the maximum available pressure drop for the valve to use and this must not be
exceeded or another pump will be needed. The usual rule of thumb is that a valve
should be designed to use 10-15% of the total pressure drop or 10 psi, whichever
is greater.
For above example step#1 system, 10% of the total pressure drop is 15 psi which
is what we'll use as our allowable pressure drop when the valve is wide open (the
pump is our system is easily capable of the additional pressure drop).


STEP #3: Calculate the valve characteristic


Step#4:-Preliminary Valve Selection

The Cv value should be used as a guide in the valve selection, not a hard
and fast rule. Some other considerations are:
a. Never use a valve that is less than half the pipe size
b. Avoid using the lower 10% and upper 20% of the valve stroke. The
valve is much easier to control in the 10-80% stroke range.

Before a valve can be selected, we have to decide what type of valve will
be used . For our case, we'll assume we're using an equal percentage,
globe valve . The valve chart for this type of valve is shown below. This
is a typical chart that will be supplied by the manufacturer.

For our case, it appears the 2 inch valve will work well for our Cv value at
about 80-85% of the stroke range. Notice that we're not trying to squeeze
our Cv into the 1 1/2 valve which would need to be at 100% stroke to
handle our maximum flow.


Typical Chart Supplied by Manufacturer.


Step# 5:-Check Cv & Stroke % at Min. Flow

If the stroke percentage falls below 10% at our minimum flow, a smaller
valve may have to be used in some cases.
Judgments plays role in many cases. For example, is your system more
likely to operate closer to the maximum flowrates more often than the
minimum flowrates?
Or is it more likely to operate near the minimum flow rate for extended
periods of time. It's difficult to find the perfect valve, but you should find
one that operates well most of the time. Let's check the valve we've
selected for our system:


Step#6:Check Gain across Applicable Flow Rates
• Gain is defined as:

•

• Now, at our three flowrates:
Qmin = 25 gpm
Qop = 110 gpm
Qdes = 150 gpm
we have corresponding Cv values of 6.5, 28, and 39. The corresponding
stroke percentages are 35%, 73%, and 85% respectively. Now we construct
the following table:
Flow (gpm) Stroke (%) Change in (gpm) Change in Stroke (%)
25 35 110-25=85 73-35=38
110 73
150 85 150-110=40 85-73=12

Gain #1 = 85/38 = 2.2
Gain #2 = 40/12 = 3.3


General Control valve Gain.
The difference between these values should be less than 50% of the
higher value.
0.5 (3.3) = 1.65
and 3.3 - 1.65 = 1.65. Since 2.2 is closer than 50%, there should be
problem with controlling the valve. Also note that the gain should never
be less than 0.50.
Turndown :- It is ratio of the calculated Cv at maximum condition to the
calculated Cv minimum.
Rangeability :- It is ratio of Cv of the valve fully open to the minimum Cv
at which it can control.
The rangebility of the selected valve must exceed the turndown
requirements of the application.



Any Question ?


01 General Control Valves Training.

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